Radioactive isotopes are widely used in industry, medicine and the life sciences. The utility and commercial value of a radioisotope are determined based upon specific activity, with a high specific activity having greater utility and value.
Currently, isotopes are produced by electron beams, ion beams, and nuclear reactors. Electron beams are now generally used to produce short-lived isotopes at locations near the site of use. Ion beams and reactors are generally used to produce longer-lived isotopes at central facilities.
Many isotopes are amenable to production by all three techniques. These include isotopes prepared by either the addition or removal of a neutron from a naturally occurring targeted isotope. Currently, the ion beam has been the method of choice for neutron removal because of its relatively high energy efficiency. However, the ion beam process is disadvantaged by its high initial cost, complexity of operation, and limited ability to be scaled to large production rates. In addition, the relatively heavy mass of the ions makes it very difficult to generate high current density beams. Furthermore, because the ion energy is deposited in a very short distance, thus causing intense local target heating, the beam cannot be sharply focused without destroying the target. This limits the average specific activity achievable by ion beams.
Electron beams have significantly longer stopping distances than do ion beams, however, electron beams must generate photons within the target before the radioisotope can be formed. Further, high electron beam power density, required to generate the photon intensity needed to produce a high specific activity of radioisotope, will typically impose unacceptably high heat loads upon a target material, resulting in target melting.
Fission reactors compete with the beam sources in the production of isotopes through neutron absorption processes and also have a unique role in the production of isotopes separated from fission products.
Fission reactors are the method of choice for neutron addition because of their ability to produce large quantities of product. However, nuclear reactors are extremely expensive, have very high operating costs and are subject to exceedingly stringent siting and operational constraints under Federal regulations.
Therefore, a need exists for a less expensive and less complex means for producing high specific activities of longer-lived radioactive isotopes.